1. Field of the Invention
The present invention relates to a process for producing polyester copolymers of cyclohexanedicarboxylic acid and aromatic diols and more particularly, to a process for producing liquid crystalline copolymers thereof.
2. Brief Description of the Prior Art
In recent years, there have been demanded materials having excellent heat resistance, rigidity or chemical resistance, etc., namely, thermoplastic resins for general purpose thermoplastic resin molded articles such as fibers, films, molded articles, etc.
Aromatic polyesters (hereafter referred to as all aromatic polyesters) prepared by condensation polymerization from aromatic dicarboxylic acids and aromatic diols meet the physical requirements described above to some extent. However, the aromatic polyesters are neither soluble nor fusible as materials and involve many problems also in moldability thereof. On the other hand, copolymers prepared from polyethylene terephthalate and acetoxybenzoic acid are known as liquid crystalline polymers (later described).
That is, polymers obtained by using cyclohexanedicarboxylic acids in place of aromatic dicarboxylic acids and condensing the cyclohexanedicarboxylic acids and aromatic diols are known (Macromolecules, 1986, 19, 1789-1796). The polymers change to liquid crystalline melts in a melt state at high molecular weight and high temperatures and can be molded into very strong fibers through spinning. In order to prepare the polymers, however, aromatic diols cannot be used directly but should be once converted into the diacetates of aromatic diols, which results in uneconomical steps.
In addition, the liquid crystalline polymers described above are insufficient in view of heat resistance since their thermal deformation temperature is 70.degree. to 80.degree. C. Further the liquid crystalline polymers are prepared by the reaction of acid chlorides and alcohols or the ester exchange method and such a process encounters a problem that it was difficult to prepare the products having constant physical properties.
The present inventors made extensive investigations to solve the foregoing problems relating to the all aromatic polyesters or liquid crystalline polymers and find economical polyesters having good heat resistance. As a result, they have first discovered that by the use of condensing agents of thionyl chloride and pyridine in combination, polyesters could be obtained by condensation polymerization of cyclohexanedicarboxylic acids and aromatic diols, preferably further using aromatic oxycarboxylic acids in combination.
Noting that these polyesters could solve the foregoing problems of the prior art, the present invention has been accomplished.
The reaction between thionyl chloride (SOCl.sub.2) and pyridine and the reaction between the reaction product and aromatic dicarboxylic acids as well as the reaction product thereof and alcohols are shown in Higashi, High Molecular Substance, vol. 35, December, page 1098, 1986 but direct polycondensation of alicyclic dicarboxylic acids and aromatic diols is not disclosed therein.